Beam convergence in velocitymodulating valve



March 2, 1965 B. B. VAN IPEREN 3,172,005

BEAM CONVERGENCE IN VELOCITY-MODULATING VALVE Filed Dec. 1, 1960 FIG. 2

INVENTOR B ERNARDUSB. VAN IPEREN United States Patent 7, 3 4 Claims.(Cl.315-S.35)

This invention relates to velocity-modulating tubes in which an electronbeam is converged electrostatically to a point inside one of twopole-pieces between which a magnetic field directed axially relative tothe electron beam is present.

In a known velocity-modulating tube of the abovementioned type, themagnetic field has a strength such that the electron beam upon reachingthe second polepiece has a diameter substantially equal to its diameterat the first pole-piece. Since the diameter of the electron beam isdeterminative of how small the wavelength may be of the cavity resonatorbringing about velocity-modulation in the electronic beam, theoscillations which can be produced or amplified by means of such avelocitymodulating tube have frequencies which are comparativelylimited.

An object of the invention is to provide a velocitymodulating tube ofthe above-mentioned type which permits of obtaining higher frequencies.

According to the invention, in a velocity-modulating tube in which anelectron beam is converged electrostatically to a point inside one oftwo pole-pieces between which a magnetic field directed axially relativeto the electron beam is present, the strength of the magnetic field isin connection with the velocity of the electron beam such that theelectron beam reaches a minimum diameter at the second pole-piece, whileinside or immediately after the pole-piece means are provided forbringing about velocity-modulation in the beam and/or extracting energytherefrom.

Since the beam, after having passed through the first pole-piece,decreases still further in diameter, it may coact inside or after thesecond pole-piece with a cavity resonator of a considerably shorterwave-length than in the event that the diameter of the beam would haveremained unchanged after the first pole-piece.

As a rule, the invention can be applied in the simplest way to avelocity-modulating tube having only one cavity resonator, i.e. a reflexklystron, but since the decrease in the diameter of the electron beam isnot permanent, but repeated periodically, it is alternatively possibleto arrange the pole-pieces a little further remote from each other andto mount another cavity resonator between them, resulting in a klystronhaving two cavity resonators.

The invention will be described with reference to the accompanyingdrawing in which:

FIGURE 1 is a cross-sectional view of a reflex klystron according to theinvention and FIGURE 2 shows a cross-section of a klystron having twocavity resonators.

FIGURE 1 shows pole-pieces 1 and 2 of a permanentmagnetic block 3. Ahollow cathode 4 emits with the aid of a focusing electrode 5 and afront side 6 of the pole-piece 1 an electron beam with contours 7through an aperture 3 provided in pole-piece 1. The minimum diameter isreached approximately at the rear side of the pole-piece 1. Severalmagnetic lines of force extending from the aperture 8 to the pole-piece2 are indicated by 9. Due to the fact that the electrons travel at rightangles to these lines of force, they are subject to a force along theperiphery of the beam at right angles to the 3,172,005 Patented Mar. 2,1965 direction of travelling, resulting in a circular movement beingsuperimposed on the rectilinear movement. However, due to the circularmovement in the axial magnetic field, the electrons encounter forcesdirected towards the axis and consider-ably decreasing the diameter ofthe beam. The beam of small diameter passes, at 19, through the gap in acavity resonator 11 which is made of copper and arranged within thepole-piece 2. After leaving the aperture 10, the electron beam slightlydiverges and is reflected by a reflector electrode 12 to the aperture 10and towards the pole-piece 1. The vacuum closures at the two ends of thereflex klystron are not shown.

The cathode 4 has a negative potential of about 1000 volts and thereflector electrode 12 has a negative potential of 300 volts relative tothe pole-pieces 1 and 2. The voltage of the focusing electrode 5 differsbut slightly from that of the cathode 4. The diameter of a hollowcathode 4 is 0.8 mm. The aperture 8 has a minimum diameter of 0.3 mm.and the aperture 10 in the cavity resonator 11 has a diameter of 0.1 mm.The electron current from the cathode is 30 mamps. The cavity resonator11 has dimensions such that the oscillations produced by the reflexklystron have a wave-length of about 2.5 mms.

The spacing between the adjacent sides of the polepieces is 1.3 mm. andthe magnetic field in the axis of the beam has a strength of about 3300gauss.

FIGURE 2 differs from FIGURE 1 only insofar that between the twopole-pieces, which now have a spacing of 4 mms. between them, anothercavity resonator 13 having an aperture 14 is provided at the area wherethe electron beam has a minimum diameter for thefirst time. The secondminimum of the diameter falls again in the aperture 10 of the cavityresonator 11. The cavity resonator 13 is supported by means of a copperblock 15 which bears on the pole-piece 2. The collector electrode forthe electrons having passed the cavity resonator 11 is indicated by 16.The wave-guides for the supply and discharge of the energy in the cavityresonators are not shown.

What is claimed is:

1. A velocity modulating tube comprising means to generate and projectan electron beam along a given direction, first and second pole-piecemembers each having an aperture through which the electron beam passes,focussing means for converging the electron beam to a point within theaperture of one of said pole-pieces, said pole-pieces definingtherebetween a magnetic field coaxial with the electron beam having astrength at which the electron beam has a minimum diameter at the secondpole-piece member, and means in proximity to the second pole-piecemember for selectively velocity modulating the electron beam andextracting energy therefrom.

2. A velocity modulating tube comprising means to generate and projectan electron beam along a given direction, first and second pole-piecemembers each having an aperture through which the electron beam passes,focussing means for converging the electron beam to a point within theaperture of one of said pole-pieces, said polepieces being spaced apartand defining therebetween a magnetic field coaxial with the electronbeam having a strength at which the electron beam has a minimum diameterbetween the pole-piece members, a first resonant cavity between thepole-pieces through which the beam passes and is velocity modulated, anda second cavity resonator in the proximity of the point at which theelectron beam has a minimum diameter through which the beam passes andenergy is extracted therefrom.

3. A velocity modulating tube comprising means to generate and projectan electron beam along a given direction, first and second pole-piecemembers each having an aperture through which the electron beam passes,electrostatic focussing means for converging the electron beam to apoint within the aperture of one of said polepieces, said pole-piecesdefining therebetween a magnetic field coaxial with the electron beamhaving a strength at which the electron beam has a minimum diameter atthe second pole-piece member, a cavity resonator in proximity to thepoint at which the beam has a minimum diameter and for velocitymodulating and extracting energy from the beam, and a reflectorelectrode positioned after said second pole-piece for reflectingelectrons in said beam passing through the aperture in the secondpole-piece member.

4. A velocity modulating tube comprising means to generate and projectan electron beam along a given direction, first and second pole-piecemembers each having an aperture through which the electron beam passes,electrostatic focussing means for converging the electron beam to apoint within the aperture of one of said polepieces, said pole-piecesbeing spaced apart and defining therebetween a magnetic field coaxialwith the electron beam having a strength at which the electron beam hasa minimum diameter between the pole-pieces and at the second pole-piecemember, a cavity resonator in the proximity of the point between thepole-pieces at which the electron beam has a minimum diameter forvelocity modulating the electron beam, a second cavity resonator at thesecond pole-piece member in proximity to the point at which the electronbeam has a minimum diameter and through which the beam passes forextracting energy therefrom, and a collector electrode disposed on theside of the second resonant cavity remote from the electron beamgenerating means.

References Cited in the file of this patent UNITED STATES PATENTS2,687,490 Rich et al. Aug. 24, 1954 2,707,758 Wang May 3, 1955 2,812,467Kompfner Nov. 5, 1957 2,829,299 Beck Apr. 1, 1958

1. A VELOCITY MODULATING TUBE COMPRISING MEANS TO GENERATE AND PROJECTAN ELECTRON BEAM ALONG A GIVEN DIRECTION, FIRST AND SECOND POLE-PIECEMEMBERS EACH HAVING AN APERTURE THROUGH WHICH THE ELECTRON BEAM PASSES,FOCUSSING MEANS FOR CONVERGING THE ELECTRON BEAM TO A POINT WITHIN THEAPERTURE OF ONE OF SAID POLE-PIECES, SAID POLE-PIECES DEFININGTHEREBETWEEN A MAGNETIC FIELD COAXIAL WITH THE ELECTRON BEAM HAVING ASTRENGTH AT WHICH THE ELECTRON BEAM HAS A MINIMUM DIAMETER AT THE SECONDPOLE-PIECE MEMBER, AND MEANS IN PROXIMITY TO THE SECOND POLE-PIECEMEMBER FOR SELECTIVELY VELOCITY MODULATING THE ELECTRON BEAM ANDEXTRACTING ENERGY THEREFROM.